Fluid-operated servomotor

ABSTRACT

Pneumatic servomotor which operates the master cylinder in a vehicle brake applying apparatus comprises a two-piece cylinder for a piston and a diaphragm. The beaded marginal portion of the diaphragm has a maximum diameter which equals the internal diameter of the cylindricsl wall of the cylinder and is sealingly clamped between the sections of the cylinder. Each section has lugs which are bent over the other section to hold the sections together.

Waited 998168 Mimi Eggstein Giorgio Eggstein, San Remo, ltaly Ernstlllcinkel Alrtiengeseilschaft, Stuttgart-Zuffenhausen, Germany 221Filed: DEC-24,1969

21 Appl.No.: 888,090

Related US. Application Data [63] Continuation-impart of Ser. No.707,734, Feb. 23,

1151 3,656,4i3 14 Apr. 18, 1972 Primary Examiner-Edgar W. Geoghegan 9 3abandone 1 AssistanIExaminer-lrwin C. Cohen Attorney-Michael S. Striker[52] [1.8. CI. ..92/98 10, 92/99 51 Int. 01 ..F0lb 19/00, Fl6j 3/00ABSTRACT [5 8] F'eld of Search i Pneumatic servomotor which operates themaster cylinder in a vehicle brake applying apparatus comprises atwo-piece cylinder for a piston and a diaphragm. The beaded marginal[56] References C'ted portion of the diaphragm has a maximum diameterwhich UNITED STATES PATENTS equals the internal diameter of thecylindricsl wall of the cylinder and is sealingly clamped between thesections of the 1 1 74 8/1939 cylinder. Each section has lugs which arebent over the other 21574300 1 1/1951 section to holdthe sectionstogether. 2,612,419 9/1952 2,742,785 4/1956 8 Claims, 4 Drawing Figuresy], f2 W PATENTEUAPR 18 m2 ,uvaau:

IN VENTOR. won/a [66572717 /ZA a lad J W w A TIDE/Vi) FLUID-OPERASERVOMOMR CROSS-REFERENCE TO RELATED APPLICATION This is acontinuation-in-part of my application Ser. No. 707,734 filed Feb. 23,1968 and now abandoned.

BACKGROUND OF THE INVENTION The present invention relates toimprovements in pneumatic servomotors, particularly to servomotors ofthe type which are actuated by means of vacuum-to atmospheric pressuredifferential and may be utilized as a booster unit for operation of themaster cylinder in a vehicle brake applying apparatus. Still moreparticularly, the invention relates to improvements in the design andassembly of cylinders or shells with pistons and diaphragms in suchservomotors.

Servomotors for master cylinders of vehicle brake applying apparatus arenormally operated by vacuum in the air intake of the engine. Suchservomotors comprise a cylinder or shell of sheet metal accommodating anaxially movable piston or diaphragm plate of sheet metal. A forcetransmitting member connects the piston with the hydraulic mastercylinder of the brake applying apparatus. As a rule, the pistonresembles a dish and is sealingly connected with the central portion ofa flexible diaphragm whose marginal portion is sealingly secured to thecylinder. Suitable valves are employed to regulate the pressure inresponse to axial displacement of the piston on application ortermination of foot pressure against the brake pedal.

In-conventional servomotors, the marginal portion of the diaphragm isprovided with a bead which is clamped in a flange surrounding theperiphery of the cylinder. As a rule, the cylinder comprises twosections whose marginal portions are secured to each other and form theaforementioned flange. The bead of the diaphragm is clamped between themarginal portions of the sections during assembly of the cylinder.Reference may be had to U.S. Pat. No. 2,742,785 to St. Clair, U.S. Pat.No. 2,969,046 to Kellogg et al. and U.S. Pat. No. 3,026,853 to Stelzer.Such mode of affixing the diaphragm to the cylinder provides asatisfactory sealing action. However, the flange increases the diameterof the cylinder without permitting a commensurate increase in thediameter of the piston. Since the space in an automotive vehicle is at apremium, it is highly desirable to take full advantage of the spaceoccupied by the cylinder of the servomotor, i.e., to design theservomotor in such a way that the external diameter of its cylinderexceeds negligibly the diameter of the piston therein. Of course, suchdesirable ratio of the two diameters should not affect movements of thediaphragm which must be free to fold itself over the internal surface ofthe cylinder in all axial positions of the piston.

SUMMARY OF THE INVENTION It is an object of my invention to provide afluid-operated servomotor which is particularly suited for use as abooster for operating the master cylinder in a vehicle brake applyingapparatus and to construct and assemble the parts of the servomotor insuch a way that it can furnish a force considerably exceeding the forcefurnished by a conventional servomotor which occupies the same amount ofspace in an automotive vehicle.

Another object of the invention is to provide a servomotor wherein theeffective diameter of the piston exceeds considerably the effectivediameters of pistons in conventional servomotors whose cylinders occupythe same amount of space as the cylinder of my servomotor.

A further object of the invention is to provide a novel connectionbetween the sections of a cylinder in a pneumatic servomotor for use inbraking apparatus of automotive vehicles and to provide a novelconnection between the sections and the marginal portion of thediaphragm.

An additional object of the invention is to provide a servomotor whichcan be utilized in presently known vehicle brake applying apparatus.

The improved servomotor comprises a cylinder including a first coversection having a cylindrical wall and a second cover section secured toone end of the cylindrical wall, a piston reciprocably received withclearance in the cylindrical wall of the first cover section, and adiaphragn having a median or central portion secured to one side of thepiston and a preferably beaded annular marginal portion clamped betweenthe two sections of the cylinder. The maximum diameter of the marginalportion of the diaphragm approximates and preferably equals the internaldiameter of the cylindrical wall on the first cover section. An annularclamping member is provided on the cylindrical wall to press themarginal portion of the diaphragm against the second cover section, orvice versa. The two sections are preferably provided with annuli ofalternating lugs or analogous projections. The lugs of one section arebent over the other section, and vice versa, to provide a reliableconnection between the two sections.

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theimproved servomotor itself, however, both as to its construction and itsmode of operation, together with additional features and advantagesthereof, will be best understood upon perusal of the following detaileddescription of certain specific embodiments with reference to theaccompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a fragmentary end elevationaiview of a servomotor which embodies one form of my invention;

FIG. 2 is an axial sectional view as seen in the direction of arrowsfrom the line ll-II of FIG. 1;

FIG. 3 is a fragmentary axial sectional view as seen in the direction ofarrows from the iine lIl--Ill of FIG. 1; and

FIG. 4 is a fragmentary axial sectional view of a modified servomotor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS adjacent to the internalsurface of the cylindrical wall 11. The

spring 4 tends to bias the piston 3 in a direction to the right, asviewed in FIG. 2, i.e., toward the inner side of the cap 2. The medianportion of the diaphragm 5 overlies the central portion of the piston 3at that side of the piston which faces the cap 2, and the diaphragmcomprises a beaded marginal portion 51 which is sealingly clampedbetween the cylindrical wall 111 and the adjacent marginal portion ofthe cap 2. The maximum diameter of the diaphragm 5 does not exceed theinternal diameter of the cylindrical wall 11. An annular fold 52 of thediaphragm 5 overlies the internal surface of the wall 11 and this foldrolls itself onto or off the internal surface of the wall 11 when thepiston 3 is caused to move axially with reference to the cylinder 1. Thefold 52 also overlies the external surface of the marginal portion 31,at least when the piston 3 assumes the axial position shown in FIG. 2.

The cap 2 is connected with a profiled annular clamping member 6. Duringassembly of the cylinder l, the marginal portion 51 of the diaphragm 5is introduced into the space between the clamping member 6 and theadjoining annulus of marginal projections or lugs 22 on the cover 2, andthis marginal portion is sealingly clamped between the cap 2 and theadjoining internal surface of the wall 11 when the assembly of thecylinder is completed. Each projection 22 has a bent-over tip 21 whichoverlies the outer side of the cylindrical wall 11 (see FIG. 2). Theslots between the projections 22 of the cap 2 receive bent-overprojections or lugs 12 at the right-hand end of the cylindrical wall 11,and the projections 12 overlie the outer side of the cap 2 in a manneras shown in H65. 1 and 3. Such connection between the sections la and 2provides a fluidtight seal at the open end of the cylindrical wall 11and insures that the marginal portion 51 of the diaphragm is properlyclamped between the cap 2 and wall 11.

F IG. 4 illustrates a portion of a modified servomotor wherein the partsare denoted by numerals similar to those employed in FIGS. 1 to 3 buteach followed by a prime. The cylinder 1' includes a front cover sectionla having a cylindrical wall 11 which is connected with the marginalportion of the cap 2. The lugs or projections 12 of the wall 11' overliethe outer side of the cap 2' and the latter abuts against one end faceof a profiled annular clamping member 6 which is welded or otherwisesecured to the internal surface of the wall 11 and has a portion whichpenetrates into the beaded marginal portion 51 of the diaphragm The foldof the diaphragm is shown at 52 and the cylindrical marginal portion ofthe piston 3' at 31'. The numeral 7 denotes a welded seam which connectsthe clamping member 6' to the cylindrical wall 11'.

The effective diameter D of the piston 3 or 3 corresponds to thediameter of the median portion of the fold 52 or 52'. It will be seenthat the diameter D is only slightly less than the maximum diameter ofthe cylinder 1 or 1. This is achieved by omitting the aforementionedexternal flange which is employed on the cylinders of conventionalservomotors. As shown in FIGS. 2 and 4, the diameter of the externalsurface of the cylindrical wall 11 or 11 in my servomotor is constantfrom end to end. Also, the thickness of the wall 11 or 11 is constant.

The advantages of my servomotor will be readily understood upon perusalof the preceding description. The output of the improved servomotorexceeds considerably the output of a conventional servomotor withoutrequiring more room in an automotive vehicle. The average diameter ofthe cylinder (not counting the flange) in a conventional servomotor isabout 150 millimeters when such servomotor is used in a medium-sizedautomotive vehicle. The cross-sectional area of such a cylinder is about180 cm The radial dimension of the flange is about 16 mm, i.e., themaximum diameter of the cylinder with the flange included is about 180mm. If the cylinder 1 or 1 of my invention has a diameter of about 180mm, its cross-sectional area is about 260 cm The useful or effectiveportions of such areas are reduced by the area between the internalsurface of the cylindrical wall of the cylinder and the central portionof the fold on the diaphragm. In a conventional cylinder with across-sectional area is about 154 cm In my improved servomotor, theeffective cross-sectional area of the cylinder 1 or 1' (namely, the areahaving the diameter D) is about 232 cm By assuming that the effectivesubatmospheric pressure is 0.6 atmosphere and by disregarding thereduction of the effective piston area which is due to the presence ofvalves, a conventional servomotor can provide a force of 93 kilogramswhereas the improved servomotor furnishes a force of l38 kilograms,i.e., an increase of 48 percent which is arrived at withoutnecessitating more room for installation of the improved servomotor.This is achieved by constructing and assembling the cylinder 1 or 1' andthe diaphragm 5 or 5' in such a way that the marginal portion 51 or 51need not extend beyond the internal surface of the cylindrical wall 11or 11' so that the flange which is considered necessary on the cylindersof conventional servomotors can be dispensed with and that the thussaved space can be used to enlarge the effective cross-sectional area ofthe cylinder and piston. Also, the manufacturing cost of the cylinder isless than in presently known servomotors because the wall 11 or 11' neednot be formed with a bulge to accommodated the bead 51 or 51' of thediaphragm.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featureswhich, from the standpoint of prior art, fairly constitute essentialcharacteristics 0 the generic and specific aspects of my contribution tothe art and, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of the claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims:

1. A servomotor, particularly a pneumatic servomotor for transmittingforce to the master cylinder of a vehicle brake applying apparatus,comprising a cylinder including a first cover section having acylindrical wall of uniform diameter throughout its length and a secondcover section; a dished piston reciprocably accommodated in saidcylinder; a rolling diaphragm having a central portion engaging saidpiston and an annular marginal portion sealingly engaging said cylinder,the maximum diameter of said diaphragm being equal to the internaldiameter of said cylindrical wall; and an annular clamping member; meanscontained entirely within said cylinder for rigidly securing saidannular clamping member to one of said sections to press the marginalportion of said diaphragm against the other section, said sectionshaving adjacent annular portions and at least one of said annularportions being provided with bent-over projections overlying the otherannular portion to thereby connect said sections to each other and tomaintain said clamping member in engagement with said marginal portion,said marginal portion of said diaphragm being pressed against theconnection of said adjacent annular portions.

2. A servomotor as defined in claim 1, wherein said rigid securing meansis constituted by a weld seam.

3. A servomotor as defined in claim 1, wherein said one annular portionforms part of said wall.

4. A servomotor as defined in claim 1, wherein said one annular portionforms part of said second section.

5. A servomotor as defined in claim 1, wherein each of said annularportions comprises bent-over projections and wherein the projections ofone of said annular portions alternate with projections of the otherannular portion.

6. A servomotor as defined in claim 1, wherein said second section abutsagainst said clamping member.

7. A servomotor as defined in claim 1, wherein said piston comprises acylindrical marginal portion which is closely adjacent to the internalsurface of said wall.

8. A servomotor as defined in claim 1, wherein said marginal portion ofsaid diaphragm comprises a radially inwardly extending bead adjacent tosaid clamping member.

1. A servomotor, particularly a pneumatic servomotor for transmittingforce to the master cylinder of a vehicle brake applying apparatus,comprising a cylinder including a first cover section having acylindrical wall of uniform diameter throughout its length and a secondcover section; a dished piston reciprocably accommodated in saidcylinder; a rolling diaphragm having a central portion engaging saidpiston and an annular marginal portion sealingly engaging said cylinder,the maximum diameter of said diaphragm being equal to the internaldiameter of said cylindrical wall; and an annular clamping member; meanscontained entirely within said cylinder for rigidly securing saidannular clamping member to one of said sections to press the marginalportion of said diaphragm against the other section, said sectionshaving adjacent annular portions and at least one of said annularportions being provided with bent-over projections overlying the otherannular portion to thereby connect said sections to each other and tomaintain said clamping member in engagement with said marginal portion,said marginal portion of said diaphragm being pressed against theconnection of said adjacent annular portions.
 2. A servomotor as definedin claim 1, wherein said rigid securing means is constituted by a weldseam.
 3. A servomotor as defined in claim 1, wherein said one annularportion forms part of said wall.
 4. A servomotor as defined in claim 1,wherein said one annular portion forms part of said second section.
 5. Aservomotor as defined in claim 1, wherein each of said annular portionscomprises bent-over projections and wherein the projections of one ofsaId annular portions alternate with projections of the other annularportion.
 6. A servomotor as defined in claim 1, wherein said secondsection abuts against said clamping member.
 7. A servomotor as definedin claim 1, wherein said piston comprises a cylindrical marginal portionwhich is closely adjacent to the internal surface of said wall.
 8. Aservomotor as defined in claim 1, wherein said marginal portion of saiddiaphragm comprises a radially inwardly extending bead adjacent to saidclamping member.